Physics, lasers and my wonderful daughter

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Monthly Archives: July 2012

I was on vacation with my family last week and did not quite manage to get this entry up on time and so missed last week. But I enjoyed the time spent with my family, visiting and traveling to new places.

There have been a lot of fires in CO this year. The dry winter, dry spring and very hot, dry and windy summer weather have made for perfect conditions for fires to spread rapidly in the forested areas of the mountains. Because of this, there is an extreme fire ban in CO to prevent more fires. This was the quietest 4th of July I can remember because many of the towns around where I live cancelled the fireworks celebrations. No one wanted to start another fire.

Unfortunately, mother nature has not been informed of the fire ban. Many of the fires this year were started by lightning strikes during one of our many dry thunderstorms – lots of lightning and thunder and little or no rain.

A few weeks ago, I went out for a walk with my daughter and looked up to see a huge plume of smoke in the sky. I immediately looked up the news to try to figure out where the fire was – not close enough to be a danger to us (other than the horrible smoke) but close enough to affect many of my friends. In the news article, it stated that the fire was probably started by lightning as 51 lightning strikes had been detected in the area.

51? Really? The curious geek in me forgot all about the fire and started to wonder how they could possible know that. I spent some time looking into lightning detectors. There are several different types, but this article mentioned ground detectors, so I wanted to know how those work.

Lightning is really cool, and of course, a little scary too. But I have always been mesmerized by watching lightning flashes on a stormy day. In order to understand how ground detectors measure lightning, let’s first think about why we can see lightning – what is causing that huge bright flash?

Lightning is caused by huge static discharges. In an electrical storm, there is a huge charge difference between the clouds and the ground. This sets up a very large electric field across the air. This basically means that there is a huge amount of energy stored that has the potential to affect the air around it.

If the charge stored is enough, the electric field starts to ionize the air around it. This means that the strong electric field can actually tear electrons off of the atoms in the air. These electrons then become free to move around (no longer tightly attached to the atoms) and this causes a current to flow through the air like it would through a metal wire. (How Stuff Works: Lightning).

Very cool! And sort of scary…something powerful enough to rip atoms apart certainly is going to do a lot of damage if it hits me!

As this energy moves through the air, this electrical energy and atom ionization emits electromagnetic radiation – light. So we see a bright flash of light. You can see a pretty picture of the lighting and its spectrum (what colors are contained in this white light) here.

The lightning also emits a characteristic lower frequency electromagnetic radiation. In order to detect the lightning, antennas are set up to detect this lower frequency radiation. For cloud-to-ground detection, a set of three antennas are set up to triangulate the signal. All three antennas will detect the signal from the lightning and by measuring the time it takes to reach each antenna, the location of the lightning strike can be determined. Visible light detection (the big bright flash!) is also used to make sure that the lower frequency radiation is really coming from lightning and not some other source. (Wikipedia)

I never knew that these types of detectors were set up around us. I think it’s really cool that lightning detectors work so well. You can even make your own basic lightning detector if you like home electronics projects.

Despite the high level of technology and engineering that goes into really effective lightning detectors, I must admit that I am still more in awe of the amazing photographers out there that can take beautiful pictures like this (Wikipedia Commons):

During our vacation, we landed twice very near a thunderstorm. Despite being quite exhausted from travel and delays with an infant, I was in awe of the beauty and power of the lightning viewed from the sky. It is an amazing thing.

Fortunately, the weather has improved since the worst of the fires in CO. While it is still dry here, daily thunderstorms have brought some rain to help things from getting too dry. Of course, these storms also tend to bring lightning. Hopefully the wetter conditions will prevent more fires, but it is still important to be careful in the late afternoons, especially in the mountains. Lightning is beautiful but also quite powerful and dangerous.

The past week or so has been busier and more exhausting than usual (with a little girl who is suddenly having trouble getting to sleep), so I missed the blog last week. My daughter’s ability to sit up and stand easily is causing her all sorts of trouble. Whenever we lay her down in her crib, she thinks she should immediately stand up and walk around her crib (still holding onto the side). She is, of course, exhausted and needs a nap but can not quite figure out that she needs to lie back down in order to sleep. Poor kid (and poor parents!).

Having found some time to myself again after a few long weeks, I decided to do some more exploring on the Frontiers in Optics website. While the full conference program will not be up for some time, there are tons of exciting invited speakers and special symposia listed for the conference. I am going to have a hard time deciding what things to go to with so much going on – one of the big challenges of the big conferences with so many concurrent sessions.

The Future of Optics Symposium is going to address the future of optics in the areas where Emil Wolf contributed the most – Inverse Problems, Coherence and Quantum Optics, Physical Optics, and Optics at the University of Rochester.

I am especially interested to hear Anthony Devaney’s talk about the Future of Inverse Problems since this relates directly to my own research in Optical Diffraction Tomography. While there are a lot of exciting areas of research dealing with new technologies in lasers, fabrication, and nanotechnology, I am always fascinated by how much there is left to learn and investigate in the very fundamental problems of optical scattering and propagation. Being able to measure the intensity profile of light after it has passed through an object and then reconstruct that object allows us to image objects that standard microscopes cannot see. And, of course, as we learn to make smaller and more complicated structures, we need ways to measure them.

This symposium seems like a wonderful way to honor a great scientist and get the younger generation excited about the exciting research that is coming up in these fields. And, speaking of the younger generation, there is another special symposium just for them: The Symposium on Undergraduate Research.

I only found out about this symposium a couple of years ago, though it has been going on for 12 years now. This is an opportunity for undergraduates to come and be involved in a large and vibrant conference. If you are an undergraduate (or have undergraduates in your lab), you should definitely look into this.

The organizer is Hal Metcalf from Stony Brook University and the deadlines for submission are at the end of the summer (instead of May) to accommodate undergraduates who usually do the bulk of their research in the summer. The symposium consists of oral presentations and post talks and the quality is really amazing – many of these presentations could easily have been given in the main conference sessions and no one would have thought they were undergraduates.

I had three students who worked with me present at this symposium in 2010 and they could not stop raving about what a wonderful experience it was. Two of my students had not planned on pursuing optics after graduation, but were so excited by the experience that one is now a graduate student in optics and the other is planning on applying for optics programs this fall.

I feel like a walking advertisement for this symposium, but I just think it is such a fantastic opportunity for undergraduates to be introduced to the vibrant optics research community. Especially for students in smaller departments who do not normally have access to these sorts of opportunities. And, of course, it is a great place for graduate advisors to recruit really phenomenal future graduate students.

Being very education and student-oriented, I think it is really cool that in addition to talking about all the current (and exciting!) research, part of Frontiers in Optics is devoted to looking toward the future of research – both in specific topics and in supporting and engaging the future scientists who will be the ones to engage in these topics.

My daughter has just started moving. We are fortunate that she started moving later than some other babies we know. We have had a blissful 10 months of not having to chase after her and put up gates in the house. Alas, that is all over now.

She is not crawling exactly, but she scoots forward. She reaches forward onto her hands while sitting and uses one leg to pull herself forward and drags the other leg behind. I have seen many of her cousins doing something similar, at pretty high speeds. This may turn into a standard crawl someday soon, or maybe not. Either way, she is definitely moving around, and faster every day.

Last week, I put her down on the floor in the bedroom so I could pick up some clothes to do some laundry. She usually goes straight to playing with our window shades, which is relatively safe. That day, though, I turned my back for just a second and she went straight across the room to the electrical outlet. Yikes! I had not yet put the safety plugs in upstairs. It is crazy how she always goes straight for the electrical outlets. They are right at eye level and are apparently quite fascinating.

So why are electrical outlets so dangerous for little ones?

First of all, can she even get her little fingers in those tiny little holes? In order for an electrical connection to be made, she needs to touch the metal connections. Even with her very little fingers, I do not think she could get them into the outlets. That being said, I certainly do not want to let her try!

I think the real danger is probably having her put one of her toys into the outlet and making an electrical connection that way. Many of her toys are plastic or rubber right now, which do not conduct electricity effectively, but she does love to play with metal things. Also, she gets into everything now that she is mobile and I let her play with anything that does not seem dangerous, so it is not unlikely that she would find something to put into that outlet.

What happens if she does manage to get something into the electrical outlet (finger, fork, etc.)? The outlet has 120 V of potential – that means that it has energy that is ready to start flowing. If you ‘complete the electrical circuit’, i.e. give that energy somewhere to flow, it will start flowing – through you.

So how much current will flow through your body if you touch an electrical outlet and what is a dangerous level? Ohm’s Law tells us that voltage, V, (that 120 V for a standard household outlet) is related to current, I, and resistance, R, through the following equation:

The amount of current that flows through us depends on our resistance to that current.

So what is our resistance? That turns out to be a complicated question because it depends on things like how dry (or wet) our hands are, and how much contact we make with the metal wires. If we connect with the wires over a large area of our bodies, our resistance is lower – it is easier for current to flow through us.

Dry skin has a larger resistance than wet skin. This is fortunate for me as a teacher. I accidently shocked myself with a 500 V source in the lab once, but my hands were covered in chalk and the contact between my hands and the wire was small. It was definitely not a pleasant shock, and I felt dizzy for a little while after, but there was no serious or permanent damage. On the other hand, I have also shocked myself on a 120 V outlet in a lab (no chalk) and it was quite painful. Who knew the life of a physicist could be so dangerous?

But I have not answered the question. What is our resistance? I had my students measure their resistance in a teaching lab using very small metal probes (small area of contact). They measured from one hand to the other and found that they had a resistance of about a megaohm – that’s one million ohms. However, an article on Electric Shock on Wikipedia cites the International Electrotechnical Commission as showing adult resistances at 100 V of ~2000 ohms. They use larger contact areas, but you never know when you shock yourself how much contact you will have, so it is much safer to assume your resistance will be low.

Okay, let us assume, to be safe, that our resistance is about 2000 ohms and the voltage of the outlet is 120 V. From the equation above (Ohm’s Law), we can calculate that this situation would send 60 milliamps (mA) of current through us. That does not sound like a lot, right? Well, an amp is a LOT of current. The same Wikipedia article cited above states that humans can feel 1 mA of current. Currents as low as 60 mA (and sometimes lower) can cause fibrillation of the heart muscles, which can lead your heart to stop.

Depending on the voltages and contact situation, electrical shocks can also cause serious burns. I had minor burns on both hands when I was shocked by the 500 V lab source. (I should note that I am always very careful around electrical sources and in both cases of being shocked, I was working with wires that had been previously damaged – a good example of why you should always have broken or old wiring repaired immediately.)

Okay, I am convinced. I should cover up my outlets and keep my daughter safe! So far we have just put in some standard outlet covers, though I have read in several places online that these covers are too easy for toddlers to remove. Fortunately, my daughter is too young to have figured that out yet (and trust me, she has tried!). As she gets older, and stronger, and more coordinated, and smarter, we may have to come up with better ways to keep her safe.

We are definitely entering a new stage of parenting. It is amazing to watch her learn to move and explore her world and I am very much enjoying it, but with every new development comes new challenges.